One of the most common secondary complications of traumatic brain injury (TBI) is substance abuse. Substance abuse affects health and function after TBI, and has been associated with worse outcomes. Deficits in self-regulation are common to both TBI and substance abuse, and may be one source of the poorer outcomes. Researchers have been hampered in their ability to study the effects of self-regulation deficits due to difficulties with measurement. Bechara's Gambling Task may provide the ideal analog for studying self-regulation and sensitivity to contingencies in persons with TBI and substance abuse, as it was originally developed to study the effects of focal damage to the orbitofrontal cortex and has been used with persons with substance use disorders. Performance on this task has shown persons with lesions in the orbitofrontal cortex to behave based on immediate consequences, without regard to the effects of their choices on future consequences. Some persons with substance use disorders show similar performance, while others appear to be extremely sensitive to rewards and under-responsive to punishment. The current project seeks to determine if the Gambling Task can be used to study self-regulation in persons with both TBI and a substance use disorder, given that the former is associated with more diffuse deficits than the group with focal lesions previously studied. Specifically, this project aims to: 1) Identify the impediments posed by co-existing cognitive deficits when using Bechara's Gambling Task to evaluate self-regulation and sensitivity to contingencies in persons with TBI; 2) Identify methods of scoring performance and describing possible underlying processes which can assist with discriminating between the performance of controls, persons with TBI only, persons with a substance use disorders only, and persons with both disorders; and 3) Determine the sample size required to detect meaningful differences in performance on the Gambling Task between controls, persons with TBI, persons with substance use disorders, and persons with both disorders.